This is a proposal requesting funds for the purpose of a JeoL 1200 electron microscope to replace an obsolescent Philips 301. A variety of studies, which demand high quality electron microscopy as a prerequisite for their success, will benefit from that acquisition of the new microscope. The proposed projects will investigate: a) the posttranslational sorting of proteins out of the endoplasmic reticulum and to cellular organelles, (b) the polarized delivery of viral glycoproteins to the plasma membranes of epithelial cells, (c) aspects of the process of ribosome attachment to the endoplasmic reticulum, (d) the distribution and functional expression of central nervous system myelin (e) the differentiation and modulation of steroid secreting cells, (f) the role of the myelin associated glycoprotein in myelination of nerves, (g) the role of a small molecular weight metabolic in cystic fibrosis, (h) the synthesis and secretion of cellular growth regulatory factors, (i) the inhibition of the complement cascade, (j) the characterization of plasmodial antigens, (k) the expression of keratins and membrane proteins during differentiation of epithelia, (1) the uptake and metabolism of vitamin E. The above projects are largely being undertaken by a number of investigators in the Department of Cell Biology, who have over the years harmoniously shared major pieces of equipment and other resources within the department. In addition, several other users from outside the department will share the facility. The proposed microscope is especially suited as a shared instrument.